The present invention relates generally to extension devices for bones and, more particularly, to those devices which are especially suited for extending a phalangeal bone in the thumb or finger of a hand.
From time to time in reconstructive hand surgery, including the problems with the congential anomalies of the hand and following certain trauma, it becomes desirable to lengthen the thumb and/or one or more fingers of the hand. More specifically, such techniques are applicable for children, both with rudimentary phalanges or shortened segments of their hand, and to adults who have partially lost their thumb but still retain the first metacarpal. The method of lengthening involves an osteotomy followed by the application of an apparatus which provides a very gradual separation of the divided bone ends, thereby adding considerable length to the specific body part. Such procedures are particularly beneficial following thumb loss in that as much as 2-3 additional centimeters of thumb length may be gained by dividing and separating the first metacarpal and subsequently interposing a bone graft; the end result being a considerably more functional thumb unit possessing an ability to pinch and grasp which was not present prior to the operation.
To this end, various devices have been designed which attach to pins driven through the bones following bone division and allow the patient to gradually distract the bony units over a period of time commensurate with the patient's discomfort and the ability of the patient's skin and soft tissues to stretch. Unfortunately, none of these devices have proved totally satisfactory in that their designs exhibit disadvantages from one point of view or another. Thus, problems with bending, jamming, corrosion, and failure to turn have been frequent. Some of these problems have resulted in a failure of the extension procedure, infection, or an inability to obtain the desired amount of bone separation.
The following patent references disclose bone extension and compression devices of a type which are generally relevant to the present invention:
______________________________________ U.S. Pat. No. Inventor Issued ______________________________________ 2,002,021 Rouse May 21, 1935 4,159,716 Borchers July 3, 1979 4,187,841 Knutson Feb. 12, 1980 3,709,219 Halloran Jan. 9, 1973 3,900,025 Barnes, Jr. Aug. 19, 1975 2,371,519 Haynes Mar. 13, 1945 ______________________________________
U.S. Pat. No. 2,002,021 to Rouse discloses a surgical fraction extension appliance designed to apply stretching or extension to the limbs, for the purpose of adjusting the fractured ends of bones in the arms or legs preparatory to the application of splice plates or similar devices to the meeting ends of the fractured bone.
U.S. Pat. No. 4,149,716 to Borchers discloses an apparatus which is apparently useful for the compression and realignment of bone structures, particularly in the correction of splay foot deformity. The apparatus discloses a U-shaped jig having axially aligned threaded and unthreaded apertures, a threaded adjustment screw engaged in the threaded aperture, and a bushing having a threaded axial passage therethrough slidably disposed in the unthreaded aperture. A threaded drill pin is engaged in the passage of the bushing and serves to pierce and traverse the boned structures and hold them in a desired position of alignment.
U.S. Pat. No. 4,187,841 to Knutson discloses a surgical tool which is apparently utilized for either compression or distraction of a fractured bone. The tool includes a threaded shaft having a pair of cap members one of which includes a short pin projecting therefrom into the bone. A second pin projects from an internally threaded sleeve which is movably mounted on the shaft between the cap members. The threaded shaft is positioned parallel with the length of the bone during use.
U.S. Pat. No. 3,709,219 to Halloran discloses a bone compression device including two arms each having a pin mounted thereon at one end. Two pairs of couplings are rotatably mounted on the arms in spaced a space apart relationship. A pair of externally threaded tightening rods are engaged in the pairs of couplings and effect relative movement of the pins by screw movement. The use of guide posts slidably mounted in aligned apertures is not disclosed.
U.S. Pat. No. 3,900,025 to Barnes, Jr. discloses an apparatus for selectively distracting or compressing contiguous longitudinal bone segments. The apparatus includes two support members each positioned longitudinally coextensively adjacent respective bone segments. The members include internally threaded and axially aligned apertures which engage an externally threaded driving rod. The apparatus further discloses the use of a single guiding rod slidably received through a second pair of aligned apertures. The guiding rod apertures are laterally spaced from the threaded apertures such that the guiding rod and driving rod are positioned on opposite sides of bone pins projecting from each member.
The closest art of which the inventor is aware, and upon which the present invention is a distinct improvement, discloses a thumb or finger stretching device having pairs of pins, each of which extend laterally through a separate pair of plates disposed on both sides of the thumb or finger being stretched. The pairs of plates are also arranged longitudinally such that a single guide rod extends through aligned apertures in each column of plates. An elongate screw also extends through each column of plates such that each screw and corresponding guide rod are symmetrically positioned relative to the pins. Further details of construction involve providing the guide rods with bolt stops at each end, providing the screws with hexagonal shaped heads for turning, and forming the plates and rods of a metal which exhibits corrosion problems. The performance of this device has been unsatisfactory, however, in that the device exhibits the bending, jamming and corrosion problems previously mentioned.